Advances in our understanding of the biological bases of learning and memory from evolutionary influences down to molecular mechanisms will inevitably lead to practical applications. Understanding how memory systems evolved in response to environmental pressures can add to our understanding of how human memory systems have taken form, and thus aid in our attempt to elevate some human memory deficits. The aim of the proposed research is to increase our understanding of the ways in which the hippocampus mediates memory formation through the study of a naturalistic model of memory formation: the storage and recovery of food (caching) in birds. Results from proposed behavioral and neural lines of inquiry will address the possibility that certain memory features have become modified during evolution in response to the selective advantage of retrieval of stored food. The comparative work proposed looks at the differences between the formation of spatial memory and memory for visual cues (1) within a food-storing species and (2) between closely related species that do and do not store food. This includes an analysis of memory formation at both the behavioral and neurobiological level by investigating (1) the effects of photoperiod on short- and long-term memory (STM, LTM) for spatial and visual cues; (2) the effect of photoperiod on hippocampal size; and (3) hippocampal involvement in STM and LTM for spatial and visual cues through the use of lesions. Results will add to our current models of the biological bases of learning and memory, hippocampal structure and function, and season-mediated brain plasticity and contribute to several areas of neuroscience including neuroethology, biological psychology, and psychopharmacology.